From the structural point of view, golf balls are generally classified into two categories: wound golf balls and solid golf balls. The wound golf balls have a rubber core containing some liquid, rubber yarn wound around the core being stretched about ten times, and a cover thereon. The solid golf balls are hard rubber solid spheres. There are solid golf balls of one-piece type and of two-piece type.
For any golf ball, the top surfaces of materials are coated with paint layer. This paint layer generally has a double layer structure which consists of a white painting layer and a clear painting layer such that the clear painting layer forms the top layer of a golf ball. Conventionally, the clear painting layer is formed by applying a clear paint of urethane resin series.
Such paint layer is required to have various characteristics. A paint layer for a golf ball is required to have excellent toughness for withstanding strong impact produced by hitting with a club face and also to have flexibility for following the deformation of the ball caused by the impact. When the ball falls down on the ground, the ball is strongly abraded with grasses, mud, fine gravels, and the like because the ball rotates. This leads to the following phenomenon that the gloss of the ball is reduced by such abrasion, that the mud enters into flaws produced therein, and that the ball is contaminated with grass axil. Nowadays, golf balls are desired to retain their white appearance and their gloss even after used. Therefore, paint layers for golf balls are desired to have excellent wear resistance and excellent scuff resistance and to be hard to be contaminated so that their white appearance and their gloss are recovered by wiping off mud and grass axil.
However, a conventional golf ball of which top surface is a clear painting layer of urethane resin is remarkably contaminated after used. In particular, oil dirt and grass axil can not be removed even being wiped with a wet dust cloth. Further, since dirt enters into fine flaws produced therein by friction and impacts, the original white appearance and gloss are hardly recovered.
Therefore, there is a need to provide a paint which is flexible and has great elongation and scuff resistance. However, if using such a paint, a resultant ball adversely has high friction on its surface. In a place, such as a driving range, where a large number of golf balls are collected and transported, too large friction may lead to plugging of golf balls in a transporting passage because the balls are in contact with high frictional force. This trouble is so-called blocking phenomenon.
Japanese patent publication H5-269221A discloses a clear paint of urethane series which contains an organic modified polysiloxane including hydroxyl group. By using the clear paint, a resultant golf ball can be provided with a paint layer having good impact resistance and high sliding property. In the above JP H5-269221A, the organic modified polysiloxane including hydroxyl group is concretely polyester modified polysiloxane including hydroxyl group Byk-370 (available from BYK Chemie Japan K.K.).
However, the paint disclosed in JP H5-269221A has following disadvantages.
The organic modified polysiloxane including hydroxyl group exhibiting a role of providing the sliding property can react with the binder resin. Since the organic modified polysiloxane including hydroxyl group has high surface activity, it easily diffuses into the surface and remains on the surface of the paint layer because of its reactivity. Because of such properties of the organic modified polysiloxane including hydroxyl group, the paint disclosed in Japanese patent publication H5-269221A shows sufficient sliding property. However, in driving ranges and the like, golf balls are often in contact with water, such as dipped in cleaning solution for removing dirt and exposed to rain. When the surface of the golf ball is in contact with water, unreacted organic modified polysiloxane including hydroxyl group or relatively low molecular weight resin components (including polysiloxane) may leach out into water, resulting in significant deterioration of sliding property. Particularly, since the organic modified polysiloxane including hydroxyl group easily remains on the surface of coated layer, it easily leaches out into water when dipped in the water. Therefore, the organic modified polysiloxane including hydroxyl group is lost due to the leaching so that the effect of the sliding property can not be maintained for a long period of time.